how do I grep in R?

Question

I would like to choose rows based on the subsets of their names, for example

If I have the following data:

data <- structure(c(91, 92, 108, 104, 87, 91, 91, 97, 81, 98),  .Names = c("fee-", "fi", "fo-", "fum-", "foo-", "foo1234-", "123foo-",  "fum-", "fum-", "fum-")) 

how do I select the rows matching 'foo'?

using grep() doesn't work:

 grep('foo', data) 

returns:

integer(0) 

what am I doing wrong? or, is there a better way?

Thanks!

Answer 1

You need to grep the names property of data, not the values property.

For your example, use

> grep("foo",names(data)) [1] 5 6 7 > data[grep("foo",names(data))]   foo- foo1234-  123foo-    87       91       91  

One other clean way to do this is using data frames.

> data <- data.frame(values=c(91, 92, 108, 104, 87, 91, 91, 97, 81, 98),                     names = c("fee-", "fi", "fo-", "fum-", "foo-", "foo1234-", "123foo-",                     "fum-", "fum-", "fum-"))  > data$values[grep("foo",data$names)] [1] 87 91 91